Polytetrafluoroethylene seals are well known for their ability to withstand the environmental conditions to which oil seals are exposed incident to sliding contact with a shaft. However, the inability to mold such seals in an efficient manner has forced the industry to turn to other manufacturing techniques. The most successful technique heretofore used comprised grooving the end of a billet of polytetrafluoroethylene and thereafter cutting the polytetrafluoroethylene seal element from the billet as taught in, for example, U.S. Pat. No. 3,857,156. Other teachings of grooving a seal are found in the patents to Jagger U.S. Pat. No. b 2,606,779 and Corsi U.S. Pat. No. 4,132,421. Slitting of the end face of a billet is taught in applicant's copending application Ser. Nos. 322,640 (supra) and 494,817 (supra). An improved slitting apparatus is taught in applicant's copending application Ser. No. 350,359 (supra).
Patents that teach the use of built-up ribs to effect hydrodynamic pumping of oil are Bainard U.S. Pat. No. 4,118,856 or Jagger U.S. Pat. No. 3,620,540. A teaching of both ribs and grooves is found in the "Journal of Teflon", pages 2-4, January 1970. However both open grooves, slits, and built-up ribs exhibit operational problems to which the present invention presents a solution.